1. Field of the Invention
This invention relates to wind turbines and energy systems, specifically to vertical axis machines and systems that have the capability to supply public energy needs in combination with existing infrastructure and equipment.
2. Prior Art
Large horizontal axis wind turbines have the lion's share of the current land based market. They also constitute the planning for off shore installations of very large (up to 5 MW) turbines. While many high value wind sites lie in mountain passes such as Tehachapi in California and Guadalupe in Texas they are limited in frequency and access to the grid. A host of attractive sites are found in the Great Plains, (called the ‘Saudi Arabia’ of wind), but lie a considerable distance from major population areas.
Just off shore of major population centers on the Atlantic, Gulf Coast, Pacific and Great Lakes lie wind energy resources that dwarf on-shore wind energy available by factors of up to 5:1. Recent DOE inquiries have focused on tall towers for islands to capture this resource. The difficulties of the Nantucket Shoals project, general use of the shoreline as a recreational/tourist resource and valid ‘not in my back yard’ sentiments of the public demonstrate the limitations of this direction of development. Another difficulty is integrating and connecting the variable off-shore wind resource to existing shore-based power plants that are the ties to the distribution grid.
As turbines get larger, the large moment of inertia in the three-blade horizontal axis design requires ever heavier composite cross-sections. Fiberglass thickness now reaches close to three inches for 1.5 to 2.5 MW production machines. The strength to weight properties of composites will limit the turbine size in the same way the size of dinosaurs was limited by the properties of bone. A planned developmental 5 MW turbine for off-shore installation in Germany will have 18 ton blades, even considering some use of high cost carbon fiber reinforcement. Production scale machines now so large that they need to be rotated whenever they pass below bridges.
Thinking in land based terms of ever larger turbines is not particularly useful within an ocean context where average wind energy can go from 500 W/m2 to 1000 W/m2 by moving slightly further off shore. The top-heavy design of horizontal axis mills and transmission to shore increases the cost of off shore installations by a factor of at least three over comparable land installations. Island installations have a more reasonable cost but are not scaleable in the sense that there are few opportunities available.
Within this context, Heronemous, (US App#2003/0168864) and Pflantz, (U.S. Pat. No. 6,100,600) have proposed gigantic, buoyed, off shore platforms for horizontal axis turbines to produce public power. Both are unique in generating hydrogen through electrolysis and utilizing heat to desalinate water; an important need in many areas. The former also features systems on the platform to produce methane, ammonia and liquid Hydrogen for transport by tender ship to shore. Placing large chemical production platforms off shore would seem to be more costly than placing them on land, and to invite the possibility of chemical spills in the aquatic environment. Working with liquid Hydrogen is just barely handled safely by NASA at the present time.
In addition to the limitations described above, the fixed position of the platforms, the ungainly array of multiple horizontal axis wind turbines and the turbulence experienced in large storms present the challenge of catastrophic failure such as that of the Putnam 1.5 MW installation in Vermont during WW II.
Also, from the perspective of public services, Bird, U.S. Pat. No. 6,083,382, presents a land based energy system using wind for water pumping to create a hydrostatic head for wind powered water purification. Most recently, a corporation formed around the work of Lackner et al (U.S. Pat. No. 6,790,430) has worked on the pollution free production of public electricity from coal. The work has been focused on the use of oil shale and is quite far from producing a viable public power system.
The first step of the Lackner process, however, (the hydrogenation of coal to produce methane), is a viable technology developed between the 1930's and 1960's (e.g. Schroeder U.S. Pat. No. 3,152,063). Implementation of the later technology, would go a long way towards the realistic goal of stabilizing global CO2 at 500 ppm (Browne), and could do so in a much shorter period of time and with better assurance of public safety than use of a totally Hydrogen based economy.
Earlier, Lawson-Tancred, (U.S. Pat. No. 4,274,010) developed an integrated horizontal axis system for producing heat and/or electricity based on hydraulic pumps to drive electric generators which in turn generate heat for storage or smaller amounts of electricity for on-site usage. Disadvantages of this approach were that heat could have produced directly from the fluid power and that the small scale of the installation could not effectively compete with utility based supply costs. In targeting direct production of heat, much of the cost and complexity of a wind system is reduced, allowing wind to more effectively compete in areas of modest wind energy resources.
In terms of ocean-based technology, Flettner (U.S. Pat. No. 1,674,169 & Foreign Patents) sailed a large Magnus effect powered ship across the Atlantic in 1925. Reducing weight on the top of the mast, a stable shipboard system was produced. In the 1980's Bergeson repeated this work retrofitting ships between 81 and 560 feet long with Magnus rotors, saving between 23 and 11% on fuel usage, (Gilmore).
These efforts did not put forward a systems approach to supplying public energy needs. Few designs have been put forward to collect off shore energy resources and deliver them by ship to shore based energy production and distribution infrastructure. The ability to do so also affords the opportunity to move to safe haven in the event of massive storms. It allows for scaleable and mobile systems that can respond to changing needs while also moving the production system for the most part out of everyone's ‘back yard’.
The original Darrieus vertical axis wind turbine design (U.S. Pat. No. 1,835,018) had the advantages of moving the mass of the generator to the bottom, reducing overall weight of the structure, being omni-directional and having a relatively high tip speed ratio and efficiency. One early limitation was that it was not self-starting.
Original designs were formed from Aluminum extrusions with more potential for damaging deformation than composites. Recently, Wallace et al, (U.S. Pat. Nos. 5,499,904 and 5,375,324), developed a composite Darrieus blade produced through the lower cost pultrusion process. This process addresses a potential problem of conventional horizontal axis blades; mold form/lay up process can leave potential voids and hidden defects formed in the heavy wall polymerization process.
Wallace still uses conventional troposkein Darrieus geometry and has many of the limitations outlined for it. Wallace proposes bending into the troposkein geometry from a straight geometry on site, avoiding the transport problems outlined above, but perhaps creating others.
Another limitation in the Darrieus design was the lack of pitch control. Modifications to the original curved blade by Drees, (U.S. Pat. No. 4,180,367), Seki, (U.S. Pat. No. 4,247,253) and others resolved the perceived needs for a self-starting machine with pitch control. Despite the advantages of vertical axis wind machines, they did not perform well in applications directly linked to the grid and are no longer produced in the US. This may have been related to speed regulation, to structural weakness in the rectangular geometry of the cylindrical straight blade arrays or to a standardization on horizontal axis machines.
Additional references are included on forms PTO/SB/08 A & B, (attached).